Apparatus and method for controlling diffusion

ABSTRACT

A method and device for reducing a dopant diffusion rate in a doped semiconductor region is provided. The methods and devices include selecting a plurality of dopant elements. Selection of a plurality of dopant elements includes selecting a first dopant element with a first atomic radius larger than a host matrix atomic radius and selecting a second dopant element with a second atomic radius smaller than a host matrix atomic radius. The methods and devices further include selecting amounts of each dopant element of the plurality of dopant elements wherein amounts and atomic radii of each of the plurality of dopant elements complement each other to reduce a host matrix lattice strain. The methods and devices further include introducing the plurality of dopant elements to a selected region of the host matrix and annealing the selected region of the host matrix.

CROSS-REFERENCE TO RELATED APPLICATIONS

The application is a continuation of U.S. application Ser. No.11/214,555, filed Aug. 30, 2005 now U.S. Pat. No. 7,727,868, which is adivisional of U.S. application Ser. No. 10/326,935, filed on Dec. 20,2002 now abandoned, which these applications are incorporated herein byreference in their entirety.

TECHNICAL FIELD

This invention relates to semiconductor devices and semiconductor devicefabrication. Specifically this invention relates to a method andapparatus of doping semiconductor regions and diffusion of dopantsduring semiconductor processing.

BACKGROUND

As the minimum feature size achievable in semiconductor manufacturingdecreases, impurity diffusion rates of dopants become a significantimpediment for achieving the desired device structures and correspondingperformances. Unfortunately there are only a limited number of possiblesolutions for this problem. As the minimum feature size decreases, thenumber of devices that can be formed in a given area increases with theinverse square of this feature size while dopant diffusion rates remainconstant. As the areal density of devices is raised, both the devicesize and inter-device distances must shrink accordingly. In addition, asdevice areas have been shrunken laterally, optimal dopant diffusiondepths have been substantially decreased.

Using current processing methods, dopant diffusion depth is largelyaffected by annealing operations, typically performed subsequent to animplant step. Thermal annealing is performed for a number of reasons,including activation of implanted dopant ions. Annealing also causesdiffusion of the dopant species. Depending on the device designrequirements and processes, the resulting redistribution of theas-implanted dopant ions can be unacceptably large.

What is needed is a method to control diffusion of dopant species in amatrix lattice. What is also needed is a device with a sharper diffusiongradient of dopant elements. What is also needed is a device capable ofwithstanding higher processing temperatures for longer periods of timewithout unacceptable diffusion of dopant elements.

SUMMARY

A method of reducing a dopant diffusion rate in a doped semiconductorregion is shown. The method includes selecting a plurality of dopantelements. Selection of a plurality of dopant elements includes selectinga first dopant element with a first atomic radius larger than a hostmatrix atomic radius and selecting a second dopant element with a secondatomic radius smaller than a host matrix atomic radius. The methodfurther includes selecting amounts of each dopant element of theplurality of dopant elements wherein amounts and atomic radii of each ofthe plurality of dopant elements complement each other to reduce a hostmatrix lattice strain. The method further includes introducing theplurality of dopant elements to a selected region of the host matrix andannealing the selected region of the host matrix.

A method of forming a doped semiconductor region is further shown,including forming a first conductivity type doped semiconductor well,including introducing a first dopant element and a second dopant elementto a selected region of a semiconductor surface. The method alsoincludes forming a second conductivity type doped semiconductor regionsubstantially within the first type doped semiconductor well, includingintroducing a third dopant element and a fourth dopant element. Themethod also includes annealing the selected region of the semiconductorsurface and controlling a diffusion rate of the first and second dopantelements by selecting a combination of dopant elements that minimizelattice strain in the selected region of the semiconductor surface. Themethod also includes controlling a diffusion rate of the third andfourth dopant elements by selecting a combination of dopant elementsthat minimize lattice strain in the selected region of the semiconductorsurface.

Methods of forming devices such as a transistor, a memory device, and aninformation handling system are also included in embodiments asdescribed in the specification below.

A semiconductor junction is also shown, including a first conductivitytype semiconductor region, wherein the first conductivity typesemiconductor region includes a first plurality of dopant elementschosen to minimize a host semiconductor lattice stress. Thesemiconductor junction also includes a second conductivity typesemiconductor region located substantially within the first conductivitytype semiconductor region, wherein the second conductivity typesemiconductor region includes a second plurality of dopant elementschosen to minimize the host semiconductor lattice stress.

A device such as a transistor, a memory device, and an informationhandling system may also be formed according to the specification below.

These and other embodiments, aspects, advantages, and features of thepresent invention will be set forth in part in the description whichfollows, and in part will become apparent to those skilled in the art byreference to the following description of the invention and referenceddrawings or by practice of the invention. The aspects, advantages, andfeatures of the invention are realized and attained by means of theinstrumentalities, procedures, and combinations particularly pointed outin the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A shows a prior diffusion profile within a doped semiconductorregion.

FIG. 1B shows a diffusion profile within a doped semiconductor regionaccording to one embodiment of the invention.

FIG. 2A shows a model of an undistorted semiconductor material accordingto one embodiment of the invention.

FIG. 2B shows a model of a doped semiconductor material according to oneembodiment of the invention.

FIG. 2C shows another model of a doped semiconductor material accordingto one embodiment of the invention.

FIG. 3 shows an example of semiconductor device according to oneembodiment of the invention.

FIG. 4 shows a flow diagram according to one embodiment of theinvention.

FIG. 5 shows an information handling system according to one embodimentof the invention.

FIG. 6 shows a block diagram of a processing unit according to oneembodiment of the invention.

FIG. 7 shows a block diagram of a memory device according to oneembodiment of the invention.

DETAILED DESCRIPTION

In the following detailed description of the invention, reference ismade to the accompanying drawings which form a part hereof, and in whichis shown, by way of illustration, specific embodiments in which theinvention may be practiced. In the drawings, like numerals describesubstantially similar components throughout the several views. Theseembodiments are described in sufficient detail to enable those skilledin the art to practice the invention. Other embodiments may be utilizedand structural, logical, and electrical changes may be made withoutdeparting from the scope of the present invention. The terms wafer andsubstrate used in the following description include any structure havingan exposed surface with which to form a device or integrated circuit(IC) structure. The term substrate is understood to includesemiconductor wafers. The term substrate is also used to refer tosemiconductor structures during processing, and may include otherlayers, such as silicon-on-insulator (SOI), etc. that have beenfabricated thereupon. Both wafer and substrate include doped and undopedsemiconductors, epitaxial semiconductor layers supported by a basesemiconductor or insulator, as well as other semiconductor structureswell known to one skilled in the art. The term conductor is understoodto include semiconductors, and the term insulator or dielectric isdefined to include any material that is less electrically conductivethan the materials referred to as conductors.

The term “horizontal” as used in this application is defined as a planeparallel to the conventional plane or surface of a wafer or substrate,regardless of the orientation of the wafer or substrate. The term“vertical” refers to a direction perpendicular to the horizontal asdefined above. Prepositions, such as “on”, “side” (as in “sidewall”),“higher”, “lower”, “over” and “under” are defined with respect to theconventional plane or surface being on the top surface of the wafer orsubstrate, regardless of the orientation of the wafer or substrate. Thefollowing detailed description is, therefore, not to be taken in alimiting sense, and the scope of the present invention is defined onlyby the appended claims, along with the full scope of equivalents towhich such claims are entitled. The term host matrix refers to amaterial as used in a composite structure such as a semiconductor matrixwith dopant impurities. One example of a host matrix includes, but isnot limited to, a semiconductor wafer. The term host lattice refers to astructure or regular pattern of atoms within the host matrix.

FIG. 1A shows a semiconductor substrate 100 with a junction 110 formedin a portion of the semiconductor substrate 100. In one embodiment, thejunction 110 is formed within a well region or pocket 112 that is alsoformed in a portion of the semiconductor substrate 100. Using priormethods, the junction is formed by introducing a dopant element to afirst region 114 using processes such as ion implantation. Processessuch as ion implantation force high energy ions into a surface of thesemiconductor substrate 100 or pocket 112. A microstructure of thesurface, after implantation, is damaged and the ions are notelectrically activated within the region of the semiconductor substrate100 or pocket 112.

To remove the damage from ion implantation, and to activate the ions, anannealing process is performed. Annealing also drives diffusion of thedopant element from the first region 114 to a diffused region 116. Usingprior methods, the diffused region 116 yielded an unacceptable depth 117as shown in FIG. 1A.

FIG. 1B shows a semiconductor substrate 100 with a junction 120 formedin a portion of the semiconductor substrate 100. Similar to FIG. 1A, inone embodiment, the junction 120 is formed within a well region orpocket 122 that is also formed in a portion of the semiconductorsubstrate 100. Using novel methods that will be described below, dopantelements are introduced to a first region 124. Following an annealingprocedure, dopant elements are driven by diffusion from the first region124 to a diffused region 126. As shown by FIG. 1B, the diffused region127 shows a steeper diffusion profile with a smaller diffusion depth127. It should be noted that FIGS. 1A and 1B are diagrams forillustration of differences between junctions in prior configurations incontrast to junctions after using the methods described below. FIGS. 1Aand 1B are not necessarily drawn to scale.

Diffusion is normally thought of as occurring by the random motion ofatoms with the energy being thermal, with the driving force being afunction of temperature and concentration. Therefore the higher thetemperature, the more rapid the diffusion rate. However, it has beendiscovered that the rate of diffusion of one element in another is afunction of not only temperature but other factors such as crystaldefects, in a specimen. For example, the rate of diffusion at grainboundaries may be over an order of magnitude greater than that in thebulk material.

FIG. 2A shows one embodiment of a host semiconductor lattice 200. Thelattice 200 is made up of a number of host atoms 210 that are heldtogether by bonds 212. Although a two dimensional lattice is shown forillustration, one of ordinary skill in the art will recognize that theconcepts illustrated in FIGS. 2A-2C apply to three dimensional lattices.In one embodiment, the host semiconductor lattice 200 is made up ofsilicon atoms. Although a silicon host semiconductor lattice 200 is usedas an example, other host semiconductor lattice compositions such asgallium arsenide, etc. are within the scope of the invention. In oneembodiment, the host semiconductor lattice 200 is structured in aregular patterned crystalline form. In a crystal, the bonds 212 arearranged in a regular pattern throughout the lattice 200. Forillustration purposes, the bonds 212 are shown with equal bond lengths214.

Although in one embodiment, all bonds 212 are substantially the samelength 214, other embodiments are included where bond lengths 214 varywithin the lattice 200 to form an energetically favorable atomicstacking arrangement in the host lattice 200. In describing a lattice200, as illustrated in FIG. 2A, individual atoms 210 can be described ashard spheres that can be stacked a number of ways. A number of regularpatterns of atomic stacking are therefore possible, some with equal bondlengths 214 and some with repeating variations in bond lengths 214,depending on the atomic composition and solid phase of the host matrix.

Dopant elements used to form the junctions in a silicon transistor aresubstantial (i.e., occupy lattice sites normally occupied by Si atoms).Since the radii of dopant ions differ from that of a silicon hostmatrix, the resulting differences in size imparts strain to the dopedsilicon region. This strain becomes especially large as the dopantconcentration is raised to the levels needed to form the necessaryjunctions.

FIG. 2B illustrates the host matrix 200 from FIG. 2A with the additionof a dopant atom 220. As discussed above, the dopant atom 220 is locatedin a substitutional lattice site. The dopant atom 220 causes latticestrain, thus distorting the regular pattern of the host lattice 200 thatexisted when the dopant atom 220 was not present. Host atom 230 has beenmoved from an unstrained position on line 232 to a strained location,thus distorting bonds 234 and 236. As can be seen from the Figure, otherhost atoms and bonds are similarly distorted. The effect of latticestrain is not limited to the host atoms directly adjacent to the dopantatom 220. Host atom 240 has been moved from an unstrained position online 242 to a strained location, thus distorting bonds 244 and 246.

Although FIG. 2B shows a dopant atom 220 with an atomic radius that islarger than the atomic radius of the host matrix atoms, a dopant atom220 with an atomic radius that is smaller than the atomic radius of thehost matrix atoms causes similar lattice distortion. Instead of thebonds such as 234 and 236 being compressed, the bonds adjacent to asmaller dopant atom are stretched, thus causing host lattice distortion.It has been discovered that such dopant-induced strains provide adriving force to cause enhanced, non-random diffusion effects. To reduceunwanted diffusion, it therefore follows that the net lattice strain ina junction should be at or near zero. In one embodiment, this can beachieved by using two or more dopants of the same type in each junctionwith at least one of the dopants having an atomic size smaller and onelarger than silicon. The percentages of each being so chosen that thenet size effect approaches zero.

FIG. 2C shows the host matrix 200 from FIGS. 2A, and 2B with theaddition of multiple dopant atoms. In one embodiment, the multipledopant atoms include a first dopant atom 250 with an atomic radius 251that is larger that at atomic radius 211 of host atoms 210. In oneembodiment, the multiple dopant atoms further include a second dopantatom 260 with an atomic radius 261 that is smaller that the atomicradius 211 of host atoms 210. In one embodiment, the multiple dopantatoms include P-type dopant atoms. In one embodiment, the multipledopant atoms include N-type dopant atoms. Examples of suitable N-typedopant atoms include, but are not limited to, arsenic (As), phosphorous(P), Bismuth (Bi), and Antimony (Sb). Examples of suitable P-type dopantatoms include, but are not limited to, Aluminum (Al) and Boron (B).Although FIG. 2C shows a host lattice 200 with two different dopantatoms, other embodiments include more than two different dopant atoms.

In one embodiment, a specific proportion of dopant atoms is furtherchosen for introduction to the lattice 200. When a specific combinationof multiple dopant atoms is used at a specific proportion, strain in thelattice 200 is reduced significantly. As shown in FIG. 2C, the largerradius 251 of the first dopant atom 250 complements the smaller radius261 of the second dopant atom 260. In contrast to the lattice distortionshown in FIG. 2B, atoms in the lattice, including both host matrix atomsand dopant atoms, are substantially lined up as in the unstressed stateof FIG. 2A. Dopant atom 260 is shown along substantially undistortedlines 264 and 268, and dopant atom 261 is shown along substantiallyundistorted lines 266 and 268. Although selected bonds such as bond 262in the doped lattice 200 of FIG. 2C may be shorter or longer than hostmatrix bonds 212, a center to center spacing 265 is approximately equalto the length of host matrix bonds 212.

Although FIG. 2C shows the larger first dopant atom 250 bonded adjacentto the smaller second dopant atom 260 this specific configuration is forillustration only. When multiple dopant atoms are selected andintroduced to the host lattice 200 in the correct proportions, latticestrain is minimized regardless of which host lattice sites the multipledopant atoms are located on. Small dopant atoms do not necessarily haveto be directly bonded to large dopant atoms. On a macroscopic scale, anaverage lattice strain is reduced due to the size of dopant atomsselected and the proportion in which they are introduced.

In a two dopant atom embodiment, the proportions of dopant atoms can bechosen by the following formula:x=(R _(h) −R _(s))/[(R _(l) −R _(h))+(R _(h) −R _(s))]

Where:

R_(h)=the atomic radius of a host atom

R_(l)=the atomic radius of the dopant atom that is larger than the hostatom

R_(s)=the atomic radius of the dopant atom that is smaller than the hostatom

x=the fraction of large dopant atoms to introduce to the host lattice

1−x=the fraction of small dopant atoms to introduce to the host lattice

For example, if the host atom has a relative radius of 2, the largedopant atom has a relative radius of 6, and the small dopant atom has arelative radius of 1, then “x” would equal 0.20 and “1−x” would equal0.80. A resulting dopant proportion would include one large dopant atomfor every four small dopant atoms. Similarly, if three or more dopantatoms are used, the proportion of dopant atoms that are larger than thehost matrix atoms should compensate for the proportions of dopant atomsthat are smaller that the host matrix atoms, while taking intoconsideration the relative sizes of the dopant atoms and the host matrixatoms.

In one embodiment for making an N-type junction, both arsenic (As) andphosphorous (P) are used as dopants. To compensate for the atomic radiiof the dopant atoms, approximately 36.37 percent of the dopantconcentration is phosphorus and approximately 63.63 percent of thedopant concentration is arsenic. In one embodiment for making a P-typejunction, both boron (B) and aluminum (Al) are used as dopants. Tocompensate for the atomic radii of the dopant atoms, approximately 23.68percent of the dopant concentration is boron and approximately 76.32percent of the dopant concentration is aluminum.

In one embodiment, introduction of the multiple dopant atoms to the hostlattice 200 includes an ion implantation process. As discussed above,following ion implantation, there is damage to the host lattice thatmust be repaired. Further, the implanted dopant atoms must be activatedto realize their desired electrical properties. In one embodiment, ananneal step is performed following introduction of the dopant atoms tothe host lattice. In one embodiment, a rapid thermal anneal process isused following introduction of the dopant atoms to the host lattice. Bychoosing a combination of multiple dopant atoms, introduced to a hostlattice at a specific proportion as described above, the post annealdoped region exhibits significantly reduced lattice strain. The reducedlattice strain significantly reduces unwanted enhanced, non-randomdiffusion effects.

One advantage of methods described above is that the methods effectivelyreduce the rate of diffusion of the doping elements in very shallowjunctions so that they can be exposed to a higher time temperatureenvelope without excessive degradation of the structure. Anotheradvantage of methods described above is that the methods sharpen ajunction profile by reducing diffusion rates at current anneal times andtemperatures. A further advantage of methods described above is thatsolubility in doped regions will be increased. Thus allowing for ahigher maximum doping level.

FIG. 3 shows one example of a device that is formed using the methodsdescribed above. FIG. 3 shows a transistor 300 formed in a semiconductorsubstrate 310. Other devices apart from transistors may also be formedusing the methods described above. In one embodiment, the transistor isfurther formed in a doped pocket 320. The transistor 300 includes afirst source/drain region 330, a second source drain region 332, and achannel region 334 separating the first and second source/drain regions330, 332. A gate 338 is formed over the channel region 334, with a gateoxide 336 separating the channel region 334 from the gate 338.

In one embodiment, the first and second source/drain regions 330, 332are formed using the multiple dopant implant methods described above. Inone embodiment including a doped pocket 320, the doped pocket 320 isalso formed using the multiple dopant methods described above. In oneembodiment, the doped pocket 320 is formed using multiple dopant atomsof a type that is complementary to the source/drain regions. In oneembodiment, the source/drain regions 330/332 include P-type dopantatoms, and the pocket 320 includes N-type dopant atoms. In oneembodiment, the source/drain regions 330/332 include N-type dopantatoms, and the pocket 320 includes P-type dopant atoms.

The following is an example of process conditions in one embodiment ofan N-type junction in a P-type pocket. Where the desired junction depthis approximately 500 Angstroms and the pocket depth is approximately2,000 Angstroms, the P pocket would be constructed using a 135 KEValuminum and a 60 KEV boron deposition. If the total concentration ofthe pocket was to be 10²⁰, then a 0.7632×10²⁰ aluminum deposition wouldbe used and a 0.2368×10²⁰ boron deposition would be used. The 500Angstrom N-type junction would be constructed using a 40 KEV phosphorusand a 70 KEV arsenic deposition. It the total concentration of thediffusion was to be 5×10²⁰, then the phosphorus concentration would be1.82×10²⁰ and the arsenic concentration would be 3.18×10²⁰.

Diffusion of dopant atoms in a junction is significantly reduced whenboth a pocket and a region within a pocket are formed using multipledopant atoms that are selected and proportioned as described inembodiments above. Junctions can be used to form devices that include,but are not limited to transistors, capacitors, etc.

FIG. 4 shows a flow diagram of a method of fabricating a junction in asemiconductor device. A first flow 400 includes operations for forming aregion using multiple dopant atoms to reduce lattice strain as describedin embodiments above. A second flow 410 is included in one embodiment toinclude forming a doped region within another doped region. Both methodsare effective to significantly reduce diffusion rates of dopant elementsduring processing steps such as annealing.

Semiconducting wafers, semiconductor devices, and IC's created by themethods described above may be implemented into memory devices andinformation handling devices as shown in FIG. 5, FIG. 6, and FIG. 7 andas described below. While specific types of memory devices and computingdevices are shown below, it will be recognized by one skilled in the artthat several types of memory devices and information handling devicescould utilize the invention.

A personal computer, as shown in FIGS. 5 and 6, includes a monitor 500,keyboard input 502 and a central processing unit 504. The processor unittypically includes microprocessor 606, memory bus circuit 608 having aplurality of memory slots 612(a-n), and other peripheral circuitry 610.Peripheral circuitry 610 permits various peripheral devices 624 tointerface processor-memory bus 620 over input/output (I/O) bus 622. Thepersonal computer shown in FIGS. 5 and 6 also includes at least onetransistor having a gate oxide according to the teachings of the presentinvention.

Microprocessor 606 produces control and address signals to control theexchange of data between memory bus circuit 608 and microprocessor 606and between memory bus circuit 608 and peripheral circuitry 610. Thisexchange of data is accomplished over high speed memory bus 620 and overhigh speed I/O bus 622.

Coupled to memory bus 620 are a plurality of memory slots 612(a-n) whichreceive memory devices well known to those skilled in the art. Forexample, single in-line memory modules (SIMMs) and dual in-line memorymodules (DIMMs) may be used in the implementation of the presentinvention.

These memory devices can be produced in a variety of designs whichprovide different methods of reading from and writing to the dynamicmemory cells of memory slots 612. One such method is the page modeoperation. Page mode operations in a DRAM are defined by the method ofaccessing a row of a memory cell arrays and randomly accessing differentcolumns of the array. Data stored at the row and column intersection canbe read and output while that column is accessed. Page mode DRAMsrequire access steps which limit the communication speed of memorycircuit 608. A typical communication speed for a DRAM device using pagemode is approximately 33 MHZ.

An alternate type of device is the extended data output (EDO) memorywhich allows data stored at a memory array address to be available asoutput after the addressed column has been closed. This memory canincrease some communication speeds by allowing shorter access signalswithout reducing the time in which memory output data is available onmemory bus 620. Other alternative types of devices include SDRAM, DDRSDRAM, SLDRAM and Direct RDRAM as well as others such as SRAM or Flashmemories.

FIG. 7 is a block diagram of an illustrative DRAM device 700 compatiblewith memory slots 612(a-n). The description of DRAM 700 has beensimplified for purposes of illustrating a DRAM memory device and is notintended to be a complete description of all the features of a DRAM.Those skilled in the art will recognize that a wide variety of memorydevices may be used in the implementation of the present invention. Theexample of a DRAM memory device shown in FIG. 7 includes at least onetransistor having a gate oxide according to the teachings of the presentinvention.

Control, address and data information provided over memory bus 620 isfurther represented by individual inputs to DRAM 700, as shown in FIG.7. These individual representations are illustrated by data lines 702,address lines 704 and various discrete lines directed to control logic706.

As is well known in the art, DRAM 700 includes memory array 710 which inturn comprises rows and columns of addressable memory cells. Each memorycell in a row is coupled to a common wordline. Additionally, each memorycell in a column is coupled to a common bitline. Each cell in memoryarray 710 includes a storage capacitor and an access transistor as isconventional in the art.

DRAM 700 interfaces with, for example, microprocessor 606 throughaddress lines 704 and data lines 702. Alternatively, DRAM 700 mayinterface with a DRAM controller, a micro-controller, a chip set orother electronic system. Microprocessor 606 also provides a number ofcontrol signals to DRAM 700, including but not limited to, row andcolumn address strobe signals RAS and CAS, write enable signal WE, anoutput enable signal OE and other conventional control signals.

Row address buffer 712 and row decoder 714 receive and decode rowaddresses from row address signals provided on address lines 704 bymicroprocessor 606. Each unique row address corresponds to a row ofcells in memory array 710. Row decoder 714 includes a wordline driver,an address decoder tree, and circuitry which translates a given rowaddress received from row address buffers 712 and selectively activatesthe appropriate wordline of memory array 710 via the wordline drivers.

Column address buffer 716 and column decoder 718 receive and decodecolumn address signals provided on address lines 704. Column decoder 718also determines when a column is defective and the address of areplacement column. Column decoder 718 is coupled to sense amplifiers720. Sense amplifiers 720 are coupled to complementary pairs of bitlinesof memory array 710.

Sense amplifiers 720 are coupled to data-in buffer 722 and data-outbuffer 724. Data-in buffers 722 and data-out buffers 724 are coupled todata lines 702. During a write operation, data lines 702 provide data todata-in buffer 722. Sense amplifier 720 receives data from data-inbuffer 722 and stores the data in memory array 710 as a charge on acapacitor of a cell at an address specified on address lines 704.

During a read operation, DRAM 700 transfers data to microprocessor 606from memory array 710. Complementary bitlines for the accessed cell areequilibrated during a precharge operation to a reference voltageprovided by an equilibration circuit and a reference voltage supply. Thecharge stored in the accessed cell is then shared with the associatedbitlines. A sense amplifier of sense amplifiers 720 detects andamplifies a difference in voltage between the complementary bitlines.The sense amplifier passes the amplified voltage to data-out buffer 724.

Control logic 706 is used to control the many available functions ofDRAM 700. In addition, various control circuits and signals not detailedherein initiate and synchronize DRAM 700 operation as known to thoseskilled in the art. As stated above, the description of DRAM 700 hasbeen simplified for purposes of illustrating the present invention andis not intended to be a complete description of all the features of aDRAM.

Those skilled in the art will recognize that a wide variety of memorydevices, including but not limited to, SDRAMs, SLDRAMs, RDRAMs and otherDRAMs and SRAMs, VRAMs and EEPROMs, may be used in the implementation ofthe present invention. The DRAM implementation described herein isillustrative only and not intended to be exclusive or limiting.

CONCLUSION

Devices and methods described above include advantages such as effectivereduction in the rate of diffusion of the doping elements in veryshallow junctions. The junctions can be exposed to a higher timetemperature envelope without excessive degradation of the structure.Another advantage of devices and methods described above is that themethods sharpen a junction profile by reducing diffusion rates atcurrent anneal times and temperatures. A further advantage of devicesand methods described above is that solubility in doped regions will beincreased. Thus allowing for a higher maximum doping level.

Diffusion of dopant atoms in a junction is further reduced when both apocket and a region within a pocket are formed using multiple dopantatoms that are selected and proportioned as described in embodimentsabove. Junctions can be used to form devices that include, but are notlimited to transistors, capacitors, etc.

Although specific embodiments have been illustrated and describedherein, it will be appreciated by those of ordinary skill in the artthat any arrangement which is calculated to achieve the same purpose maybe substituted for the specific embodiment shown. This application isintended to cover any adaptations or variations of the presentinvention. It is to be understood that the above description is intendedto be illustrative, and not restrictive. Combinations of the aboveembodiments, and other embodiments will be apparent to those of skill inthe art upon reviewing the above description. The scope of the inventionincludes any other applications in which the above structures andfabrication methods are used. The scope of the invention should bedetermined with reference to the appended claims, along with the fullscope of equivalents to which such claims are entitled.

What is claimed is:
 1. A semiconductor device, comprising: a firstconductivity type semiconductor region, wherein the first conductivitytype semiconductor region includes two or more first dopant specieshaving different atomic radii chosen to minimize a host semiconductorlattice stress; and a second conductivity type semiconductor regionlocated substantially within the first conductivity type semiconductorregion, wherein the second conductivity type semiconductor regionincludes two or more second dopant species, different from the firstdopant species, chosen to minimize the host semiconductor latticestress, the two or more second dopant species having different atomicradii.
 2. The semiconductor device of claim 1, wherein the first dopantspecies include arsenic (As) and phosphorous (P).
 3. The semiconductordevice of claim 2, wherein the first dopant species further include athird dopant species.
 4. The semiconductor device of claim 1, whereinthe first dopant species include aluminum (Al) and boron (B).